Antioxidant Action of the Antiarrhythmic Drug Mexiletine in Brain Membranes

Abstract

Mexiletine is a class Ib antiarrhythmic drug used in the treatment of ventricular arrhythmias. The Na⁺ channel blocker mexiletine inhibits calcium influx in cells via decreasing reverse operation of the Na⁺-Ca²⁺ exchanger. Thus this drug is shown to protect the CNS white matter against anoxic/ischemic injury. The aim of our study was to investigate if this drug could act as an antioxidant drug as well. The antioxidant action of this drug was studied under different oxidant conditions in vitro, and thiobarbituric acid - reactive substances were measured to follow lipid peroxidation. Mexiletine inhibited iron-ascorbate-H₂O₂ - induced lipid peroxidation in brain membranes, liver microsomes and phospholipid liposomes, being most effective in brain membranes. The inhibition was dose- and time-dependent. Mexiletine also inhibited copper-ascorbate-H₂O₂ - induced lipid peroxidation but to a lesser extent. It is concluded that mexiletine has a dual effect toward oxidative injury in brain, both by inhibiting Na⁺-Ca²⁺ exchanger-dependent Ca²⁺ influx and by acting as an inhibitor of lipid peroxidation. However, as this drug is effective at millimolar concentrations, it should be considered less active than natural antioxidants that are effective at micromolar concentrations.